NATIONAL RADIO ASTRONOMY OBSERVATORY ARCHIVES

Papers of Woodruff T. Sullivan III: Tapes Series

Note: The interview listed below was either transcribed as part of Sullivan's research for his book, Cosmic Noise: A History of Early Radio Astronomy (Cambridge University Press, 2009) or was transcribed in the NRAO Archives by Sierra Smith in 2012-2013. The transcription may have been read and edited for clarity by Sullivan, and may have also been read and edited by the interviewee. Any notes added in the reading/editing process by Sullivan, the interviewee, or others who read the transcript have been included in brackets. If the interview was transcribed for Sullivan, the original typescript of the interview is available in the NRAO Archives. Sullivan's notes about each interview are available on the individual interviewee's Web page. During processing, full names of institutions and people were added in brackets and if especially long the interview was split into parts reflecting the sides of the original audio cassette tapes. We are grateful for the 2011 Herbert C. Pollock Award from Dudley Observatory which funded digitization of the original cassette tapes, and for a 2012 grant from American Institute of Physics, Center for the History of Physics, which funded the work of posting these interviews to the Web.

Please bear in mind that: 1) This material is a transcript of the spoken word rather than a literary product; 2) An interview must be read with the awareness that different people's memories about an event will often differ, and that memories can change with time for many reasons including subsequent experiences, interactions with others, and one's feelings about an event.

Sullivan

Ok, this is talking with Professor Jesse Greenstein at his home in Pasadena on 22 August í75. Now can you just tell me very briefly where you got your degree and this sort of thing, and when you first heard about radio waves in this context?

Greenstein

I got my bachelors at Harvard in Ď29 and my masters in Ď30, and then because of the worldwide depression, returned to my family's business in New York City, for four years. In was during these years actually that [Karl] Jansky as working and by some strange coincidence I spent most of my summer holidays [Greenstein: with my family] on the Jersey seashore. I knew nothing about Jansky, but I visited the large long-distance radio telephone station which is in the sand barrens of [Greenstein: central and southern] New Jersey, just inland from the seashore. I met my wife there incidentally at this time. At the period when the discovery was made, I knew nothing about it, except that I returned to Harvard, married, and ready to get a Ph.D... [Greenstein: Except that I married, and returned to Harvard to get a Ph.D.]

Sullivan

Which year was this now?

Greenstein

1934. Four years after my masters. Janskyís work had appeared and in addition the general realization of the importance of interstellar matter in solid form, in dust, had come to astronomy.

Sullivan

Right.

Greenstein

As a result, my thesis work, which was going to be on the [Greenstein: observations of the reddening by] interstellar matter, the theory of the scattering of light by small particles, and the effect of this on the color, brightness, and numbers of stars in our Galaxy. This is ultimately connected with the structure of our Galaxy. It happened to be in an area in which [Greenstein: we knew little of] the question of what the gas in space might be doing, [Greenstein: an area] of particular excitement and importance. So although my thesis, which involved mathematical computations of multipole scatterings [Greenstein: and absorption by] of small spherical and later ellipsoidal particles, which fourteen or fifteen years later led to the theory of interstellar polarization in [Greenstein: by dust in] magnetic fields. This, oddly enough, kept hovering on the edge of what was the gas in space like and how could we find it. My thesis advisor, Bart Bok, [Greenstein: who later became the pioneer in radio astronomy] became interested in pioneering radio astronomy at Harvard but on my oral examination, in 1937, I had very interesting questions from Harlow Shapley, who asked me how I could find neural hydrogen in space.

Sullivan

Really?

Greenstein

He thought it would be interesting to know and I said, "Well, we knew how to find ionized hydrogen and diffuse nebulae, but neutral hydrogen could never exist in excited levels which we could detect in the optical region." But itís true that I did say, although just as far out kind of dream, that in a sense there might be continuity in the populations of the higher levels of the hydrogen atom with the ionized state and in fact, in the [Donald H.] Menzel notation, he wrote population numbers in the terms of the number of ions and so that since there were long wavelength transitions, it was conceivable that someday you would find them , and that they would be similar in intensity to the recombination emissions [Greenstein: in lower levels] of the ionized hydrogen, which was then well known. That was a very interesting lucky guess but I had no idea at all about the 21 cm line, of course. [Greenstein: That required non-existent physics]

Sullivan

And you never worked out what the frequencies might be or...

Greenstein

Well, yes, Iíll come to that, that was ten years later oddly enough in a paper written in Jersey [Greenstein: with Grote Reber] but nevertheless, it did occur [Greenstein: to me earlier] as a possible extension by the classical correspondence principle, that anything you knew about the continuum you knew about discrete transitions and that they were similar in intensity. Well, the free-free radiation, as we call it, hyperbolic transition, or bremsstrahlung of one kind or another was in the back of my mind, but that was about all at that time. Now, Iíd gone through three years at Harvard. In between [Fred L.] Whipple and I, somehow- and I have no real memory of how this happened- got interested in the paper by Jansky which was not in the usual electrical engineers journals...

Sullivan

In Popular Astronomy?

Greenstein

Yes. So as a result of that, Whipple, who was, I think, an instructor and I, a graduate student, sort of sat down and tried to see whether what we knew about interstellar dust might be relevant, because it was clear that if Jansky had found anything, he had found the center of our Galaxy. And the center of our Galaxy might be, thereís no reason to expect it, it might be a thermal radiator. This stupid [Greenstein: electrical engineering] unit in which the early work was published, which was something like microvolts [c.s.u] per meter mislead us. Whipple and I hadnít the faintest idea what that meant in sensible C.G.S units. So we thought, well, weíll at least take a look- had we known how to turn microvolts per meter into an equivalent temperature, we wouldnít have even started.

Sullivan

But let me ask you, you were already thinking interstellar matter, you apparently...

Greenstein

Immediately, I mean it couldnít be stars, I think, it was clear it couldnít be stars. [Greenstein: Why not the sun, so much closer?] But one thing from my study of interstellar dust, we knew the temperature of interstellar dust was around the black body 3į radiation. As you know, itís an odd coincidence [Greenstein: compared to its size], Itís the same temperature as the cosmic background. Next, that dust could not radiate with great efficiency at very long wavelengths [Greenstein: compared to its size], by Rayleigh scattering, essentially itís a terribly inefficient radiator and nevertheless, it would be interesting if you could heat dust up a lot hotter than 3į. By the way that 3į figure [Greenstein: for dust temperature] comes very simply from stellar statistics- what fraction of the sky is covered by stars, what is 1/? of the dilution factor.

So this, I think, we were too ignorant of radio-frequency engineering to have an idea of what we were trying to do. But since there was a signal [Greenstein: strength given], and we thought weíd eventually get around to finding out what it meant and the paper that Whipple and I wrote would in Proceedings of the NAS, which was a terrific disappointment. It came about because at that time, [Subrahmanyan] Chandrasekhar and the Russian [N. A.] Kosirev, who was a madman as you know, still did good work, has developed the theory of the radiative equilibrium for large bodies in which the curvature of the layers has to be taken into account. In an ordinary stellar atmosphere is thin compared to a stellar radius and the [Greenstein: curved] layers are temperature stratifies. The temperature drops 20%-30% of the reversing layer to the edge of the star. But in a large star [Greenstein: with curvature], you would have a temperature gradient which was almost very limitless. And Cecilia Payne [Gaposchkin] tried to explain the spectra of supernovae as expanding shells with curvature, which would give a very non-black body continuous spectrum. So we developed this radiative transfer theory. I was interested in it, I knew enough about the mathematics of it [Greenstein: radiative transfer], although it was all brand new. 1934, I think, when the first papers on curved atmospheres appeared. First we got the dust, I think, up to about 800į, if you assume there was dust in our galactic center and that like other galaxies, we had a very bright nucleus, and if you said you put enough dust in so it was essentially completely absorbed, the dust would heat up and that was about the right number. Though, in fact, very few dust clouds get up much above a few hundred degrees. At least, it [Greenstein: the first answer] was way above 3į. And then we went to George Washington Pierce- Is this a story youíve heard?

Sullivan

No.

Greenstein

Pierce?

Sullivan

No, I havenít heard it.

Greenstein

Do you know who he is?

Sullivan

No.

Greenstein

G.W. Pierce was the head of the Electrical Engineering Lab, I think it was called Cruft Lab at Harvard. He was the only live electrical engineer [Greenstein: Iíd ever met] and heíd written a textbook on electromagnetic waves. And we tried to go through that and there were all these stupid units. And we went to G.W. Pierce and he sort of misunderstood what we said about the signal, and he said, "Gee, thatís about... convert it to CGS youíd divided it by so and so." And so we got very excited because if it was right and our 800į radiation would have explained Janskyís observations. The only trouble was that we were wrong by whatever it is the 300...

Sullivan

Oh, the 300 ohms.

Greenstein

Something.

Sullivan

The impedance of free space.

Greenstein

Free space, exactly. We hadnít put that in. We were so excited and so ignorant that when we got this numerical coincidence, we got in touch with the public relations office- I was only a graduate student, I think Fred Whipple was an instructor- this was going to be a big deal. We got the reporters, the Harvard press bureau, whatever it is called, and then, just a day or so before the paper was to appear in its original form, we went to talk to Pierce again and he said [Greenstein: told us] we were crazy.

Sullivan

Are you saying the day before it was going to appear in the Proceedings of the NAS?

Greenstein

No, no. Before it was going to appear as a public-relations release in the Boston Evening Transcript and the Boston "this or that," and the New York Times. All of this. We were out by this incredible factor; we were actually out by more, it turned out. We had come close with the original version of it, but as you know, at long wavelengths, the temperature [Greenstein: as indicated by a flux] gets higher and higher, and so we were just plain wrong. And then as they got [Greenstein: observed] it at other frequencies later, it was clear that we would have been infinitely wrong.

Sullivan

This was in 1936 or 1937?

Greenstein

Well, the year before this paper finally appeared. Fred Whipple got sick to his stomach, I felt pretty bad, and we stopped the press release, but oddly enough, I think I have somewhere upstairs an editorial in the Boston Evening Transcript said, "Two young astronomers try to explain the mysteries of cosmic static- they were wrong by, letís say, 1000 but at least it was a noble try!"

Sullivan

Oh, Iíd like to see that.

Greenstein

I have that somewhere; I think I have it here. But it was all sort of fun and then, of course, sick as we were, we went back through it and then realized that we had just not understood the problem [Greenstein: the signal strength well enough], and one other thing we really hadnít understood is the concept of effective gain, you see. We had taken the area as essentially a wave length, I think we took- it was long waves, and it wasnít all that wrong, but of course, the effective...

Sullivan

It was really two wavelengths long? In fact, the area is probably something like 2λ2.

Greenstein

Yes, there are other errors, and so that made the signal even weaker- we had just taken it as a wavelength. By the time we finished, the very disappointed paper that actually came out [Greenstein: in the Proceedings of the NAS] showed we were just plain unable to explain it [Greenstein: the signal].

Sullivan

But Iím curious why you wanted to make such a big deal of it. Did you know that Bell Labs had had a big press release and all this thing?

Greenstein

Oh, no [Greenstein: Possibly Shapley had arranged for a public-relations triumph]. By this time Iíd read all of Janskyís papers in the IRE and stuff like that. Weíd gone into the subject professionally, the only thing that we had done unprofessionally is not understand, I guess, itís MKS [Sullivan: units].

Sullivan

But why...

Greenstein

You mean why...

Sullivan

Why the press release?

Greenstein

Well, because we were...

Sullivan

That wouldnít be the normal thing.

Greenstein

Well, actually I guess it was probably because cosmic static was a rather romantic idea. The public viewed it as romantic [Greenstein: because everyone had a radio and was impressed by the first new technology] and I think for a sensible young astronomer- letís see, letís call in í36, I was 27- the idea of seeing anything about the center of our Galaxy directly with cosmic static was romantic. Consider that my thesis work, for example, indicated that we would never see the center of our Galaxy. We estimated the absorption in those days at about a magnitude per kilopersec and we thought it would be 10 magnitudes to the galactic center. Well, thatís [Greenstein: a transmission of only] 10-4 - nothing would come through- and nothing does until you get to the infra-red, as you know. So all of this indicated that interstellar absorption blinded the astronomer at optical wavelengths to the center and here was this challenge that the only thing Jansky saw was the center.

Sullivan

Right.

Greenstein

You see, later, Reber saw a Cygnus spiral arm as a first extra thing. But this episode was just plain irritating; you know, when youíre 27 and fairly competent, you think, there is a kind of deep-seated irritation in your skin from then on, a sensitivity that here is something which we could not do and nobody thought of anything but optical wavelengths.

Sullivan

And so you were really excited?

Greenstein

Excited and challenged...

Sullivan

Excited at solving the problem of getting to the center?

Greenstein

We had almost solved it and yet obviously we were wrong.

Sullivan

But now the other question is, as you said, why did you and Whipple get interested in it? Were any of the other astronomers at Harvard interested in this?

Greenstein

Not to my knowledge, though I think Bart Bok, who was my thesis advisor and who was a very non-theoretical person and non-modern in those days, having been training in the Dutch school of classical star-count analysis, probably did egg me on, at least. But Whipple, I think, I approached mainly because he was one of the youngest of the faculty, probably the youngest who was in any way interested in trying something new. [Greenstein: We do not acknowledge help or encouragement from anyone, in our printed paper.] I had also had, I guess, a childhood interest since I had been a radio amateur. I donít know if Whipple had or not, but in any case, it was just that we paired off the way you do with a young instructor and a graduate student and tried to do this and it was a terrible blow of an emotional kind that we couldnít, because we were so sure we had. And from then on, I refused to talk to students about MKS, I donít know what an ESU is. What isnít CGS- damn it! And I stick with that. And now weíre going to flux units, Fs; and you want watts per square meter per hertz and I was ergs per square centimeter per cycle per second, and Iíll be darned if Iíll change. No, Iím serious, it really hurt.

Sullivan

There may be other cases where it has, too.

Greenstein

You just feel that something that you should have known- no, Iíll put it another way- had we known what the units meant, we would have given up, because there was nothing that would heat interstellar matter up to 100,000 degrees. There was nothing- you knew that the gaseous nebulae were at 10,000 degrees. There was nothing- you knew that the gaseous nebulae 10,000 degrees. It was the same time that Menzel, [Robert Horace] Baker, [Leo] Goldberg, and Ellen were working on the problems of diffuse nebulae and planetary nebulae and the electron temperature was always 10,000 degrees. So you couldnít even get gas at the center of the Galaxy hotter, and it wasnít an emission nebula anyway. So this stuck, and the irritation stuck and the fact is that I stayed in interstellar matter. I left Harvard and started observing with [Louis G.] Henyey the spectra of reflection nebulae which had something to do with my thesis, and also the reflection of emission nebulae, using with the nebular spectrograph, was invented by [Otto] Struve, and used first by Henyey and myself. And with that, we found various well-known properties of the diffuse nebulae, [Greenstein: the ratio of gas and dust, the high albedo of the dust, its forward-throwing phase function.]

Sullivan

This is at Yerkes?

Greenstein

At Yerkes. And then the year or so after that, with the success of Yerkes, where it was a jury-rigged thing, Struve built this rather bigger one [Greenstein: nebular spectrograph] which was moved to McDonald [Observatory], with the same optics, and with it came the HII results, the diffuse HII regions were found by Struve, ultimately explained theoretically by [Bengt Georg Daniel] StrŲmgren. So it was the interstellar gas at 10,000 degrees we kept finding. It just got us nowhere with the radio measures.

Sullivan

Which is up in the millions, but let me go back a little bit.

End of Tape 39A

Sullivan Tape 39B

Sullivan

22 August í75. So this 800 Kelvins that you just mentioned was...

Greenstein

Was our idea of what Jansky had found- it was wrong in many ways.

Sullivan

And you were able to make your model such that you got to it.

Greenstein

But [Greenstein: the model was] beyond reason, that was almost beyond reason.

Sullivan

But what you finally published was only 30 Kelvins.

Greenstein

Yes, and that was strongly heated up appreciably over what it would be in our neighborhood, [Greenstein: i.e. 30 Kelvins], by a factor of 104 increase, you see, in energy density. And thatís a lot. And to do that we had to trap the whole radiation of a center of a galaxy in an efficient dust cloud. The other part of it was that we then also knew that if you used very small particles, which my thesis had been about, which would scatter light, because they were smaller than a λ of light, theyíre terribly bad radiators [Greenstein: at radiofrequency]. So you had to then take into account the fact that you would have a few, but not many, large particles- they would be better radiators, but there wouldnít be enough of them to do a paper. So the whole thing came out as a pretty dismally- you know, if you read the paper, it should never have been published, because it didnít get anywhere, but it had been started with high hopes and it seemed at first to have worked.

Sullivan

But now were you at all concerned with the relatively high radio emission detected at high galactic latitudes? You didnít have a contour map, did you?

Greenstein

No, all we knew was Jansky- thatís in the í30s, remember.

Sullivan

Right, but you can look at his traces and see that there is stuff outside of the center; it takes a little bit more reduction, which only Reber did later, and you could have seen that at high latitudes the radiation is only maybe 1/10, 1/20 of what it is at the center, and of course, your stellar density and so forth would be way down.

Greenstein

Yes, That would sure hurt it. Well, if it is down 1/10th and if it were thermal radiation from an optically thick cloud, I imagine that would be, it would have had to be optically thick, letís say a couple of kiloparsecs from the plane, which is actually unreasonable. The other thing that sort of choked off any serious consideration of the dust model, I think, was the fact that there was very little evidence of dust in the center of galaxies, in the normal sense of galaxies. As you know, there is an enormous excess of dust right in the heart of Seyfert galaxies, and maybe in quasars, M82, and so forth. But we didnít know that at the time.

Sullivan

Right.

Greenstein

So you did, where you might have pushed this model to higher temperatures right at the center had you really known, the fact was that since I was supposedly an expert on interstellar dust, I could see that in other galaxies. There wasnít much dust. And we didnít, by the way, have a clear picture of what the center of our Galaxy was like.

Sullivan

Sure.

Greenstein

Well, worse than that, it was still a time when it wasnít certain that our Galaxy was like other galaxies. You may not realize...

Sullivan

It was not accepted that we were in a spiral removed from the center completely, you mean?

Greenstein

Well, but that the real trouble was that there was still a hangover from the time when people didnít take interstellar dust very seriously. As a result of which, we seemed to live in the Kapteyn universe, way off at the edge, [Greenstein: a few kiloparsecs in diameter, and] the globular clusters were centered 30 kiloparsecs away and our [Greenstein: local, Kabferyn] system was a kiloparsec or two diameter, and there was the idea maybe that we lived in a [Greenstein: metagalaxy, a] cluster of galaxies, where the globular clusters sat around some other [Greenstein: massive, distant] object, not our spiral but something else. And you have no idea how ignorant astronomy was at any time in the past- nor how ignorant it is now.

Sullivan

Right, unless youíve been there.

Greenstein

I think itís right to say that this failure only caused me to be permanently interested in continuing in astronomy, and so...

Sullivan

Let me just ask another question before you go on. Were you at all aware of the abstract which R.M. Langer published at an APS [American Physical Society] meeting. He presented a talk on Janskyís measurements might be due to transitions, quantum transitions in dust, charged dust particles.

Greenstein

No, thatís the thing I referred to only much later [Greenstein: 1947].

Sullivan

You knew nothing about it at the time.

Greenstein

Nothing at the time. What year was that?

Sullivan

1936.

Greenstein

Okay, just the same time, and I wasnít at the meeting [Greenstein: of the APS where he talked] and I didnít hear about it, but we [Greenstein: Reber and I] looked into it when we wrote the review [Sullivan: 1947], because then it [Greenstein: radio astronomy] was getting to be a well documented subject.

Sullivan

So you got to Yerkes then and what was your next contact with radio astronomy?

Greenstein

Well, the next thing was that since we now knew a lot about emission in the continua of gaseous nebulae that were ionized, the recombination emission on level 3 gives us the emission you see in the visible region, recombination on level 2 gives the emission beyond the Balmer limit. I studies that and wrote a couple of papers on the Orion Nebula and similar objects and this question of the continuity of this emission with the radio frequency kept coming up and at some time, and I donít know exactly the sequence, Grote Reber wrote a paper, or gave a talk, and you can tell the date better than I, in which he said that maybe the radio emission was due to charged particles...

Sullivan

Right. This was in the Proceedings of the IRE again, in 1939 or 1940.

Greenstein

1939. Okay.

Sullivan

And at the end, well he actually tried to work some of the theory using [Arthur] Eddingtonís old thing, and he forgets about the Gaunt correction factor.

Greenstein

Thatís right. Okay. Well, we heard about this and I donít actually honestly remember when I met Grote, whether he told me about it or not, but as a consequence of his statement, and itís clear because itís quite a few years later, thereís a letter Nature by Henyey, myself, and [Philip Childs] Keenan and free-free...

Sullivan

Thatís in 1946, I think.

Greenstein

Greenstein: In 1946. And thatís a long interval, with the war in between, and thatís the obvious reason for it. And the point was that we knew Reber by then, and I think by the way, Iím not sure, but I think in that paper in the Nature article, we mentioned something about the recombination lines of large N. Iíd forgotten that. Iím not sure.

Sullivan

[Sullivan: I donít remember that; Iíll check. [Greenstein: Wrong]]

Greenstein

But because all of this was really still this argument on continuity; we knew there were free electrons and therefore, but the trouble was by then two things had happened...

[Interruption]

Greenstein

That radio frequency emission was too hot, because the moment that Grote had moved to slightly higher frequencies, it was getting hotter and hotter. Everybody was out of business, because 10,000 was not enough. So I think the actual genesis, even if itís not in the paper- that idea about computing the free-free emission from the interstellar gas at 10,000į to see if it would account for the radio emission- was that we had thought of it as the confluence of the high lines. Itís odd to think of how everything goes backwards at the time, but since classical physics was the way weíd been trained, and quantum physics was a late addition, you treated everything, especially high quantum numbers and continua with a classical approximation. All you had to do was say the interval between lines was 2hR/N3dn - that was it. So everything was started on the backward side. And of course, with people chasing the temperature hotter and hotter, it made this whole effect fairly futile, but at least we went through it.

Sullivan

But now weíve skipped ahead a bit. Reber made the suggestion in the Proceedings of the IRE...

Greenstein

And somehow we knew about it.

Sullivan

Right.

Greenstein

I met Reber and to be honest, I think I met him in 1942; he was a hanger-on at the University of Chicago. He never finished college, do you know that?

Sullivan

No. I havenít talked with him; Iíve got to spend a lot of time with him.

Greenstein

He never finished college. He had a great resistance to formal education. He thought anybody who did theory was a nut- that you had to go out and measure. And he told me many years later, and I think the tragic fact about him, the reason he went to these very long wavelengths, went after things that seemed of little real interest, to me at least, was that long wavelengths was where the power was- since everything was a 1/power; there was more power at low frequency, so you want to look at lower and lower frequencies. Anyway he was a very peculiar, interesting, eccentric, individualist, scientist of the great "inventor" tradition. Somewhere, somehow, out of his work -I think, he worked for Admiral Radio, or Emerson Electric- [Greenstein: he got equipment.]

Sullivan

He worked for many different companies.

Greenstein

But during the war, somehow he built up his stuff.

Sullivan

Okay, but now were you involved at all when the paper arrived at the Astrophysical Journal?

Greenstein

Which? When are we talking about?

Sullivan

Well, 1940 this was published finally. As essentially the same paper that he published in the Proceeding of the IRE- once again, he wanted to communicate with the astronomers.

Greenstein

Yes, and thatís the one which has a kind of contour map? Or is...

Sullivan

No this only has a rough run with longitude- just a few points.

Greenstein

Yes.

Sullivan

It was only í44 when he finally...

Greenstein

I was involved with the í44 one, the Ď40 one...

Sullivan

This is the one where the apocryphal story where Struve sent Kuiper down to see...

Greenstein

I thought that the 1944 paper.

Sullivan

No, thatís the 1940 paper, the very first one because, you see, he didnít know what to do with this first...

Greenstein

I donít know why. Then the apocryphal story is really apocryphal because I think I can tell you something that will at least say what it was. Now Chandrasekhar might know, but I donít think he would care to tell; maybe I could write him and ask him- I just saw him. Chandra ran the journal with an iron hand.

Sullivan

But Struve was the editor.

Greenstein

Was Struve the editor then?

Sullivan

In 1940.

Greenstein

All right. Boy, you really have me on history because I was there through all of this and I donít know dates and times.

Sullivan

Well, Bart Bok has told me his version of this story in 1940, and also...

Greenstein

He says itís the 1940 paper?

Sullivan

Right. And also Keenan, I talked with him and he gave me his version of it. You might be interested to know that what had happened is that itís not clear exactly how, but what the agreement was, "All right, weíll publish your paper- you seem to really know what youíre doing, but leave the theory to us," and so they chopped off that free-free, and then Henyey and Keenan in their 1940 paper worked it out properly, and so these two papers appear together in the 1940 Astrophysical Journal.

Greenstein

I see. Thatís interesting, and it may be that I even knew it, but I didnít remember.

Sullivan

But you werenít involved in this episode.

Greenstein

No, no. The business about making sure whether he was turning some dial on the back I find a little hard to believe.

Sullivan

I never heard that.

Greenstein

Oh, that...

Sullivan

You mean people really thought it might be a fraud?

Greenstein

Yes, that is the story that I thought involved [Gerard] Kuiper, and the reason you see, that I attributed in to the later [Greenstein: 1944] paper is that Kuiper worked at Harvard in the same electrical engineering lab [Greenstein: which had G.W. Pierce.]

Sullivan

Oh, really.

Greenstein

Working on "Window." Being a classical physicist, I mean a classical astronomer/classical physicist in training, things like dipole scattering were things that Kuiper would know. And he was, I thought, involved in finding out whether Reber was a fraud or not, because he knew something about radar high frequency work.

Sullivan

And measurements?

Greenstein

And measurements. And therefore, I thought, it was at that occasion that it was suggested that he go down and watch the needle moving.

Sullivan

Maybe there was a double visit. But certainly Struve himself in a Sky & Telescope article in 1948 describes this initial visit with Kuiper going down, but there may have been other visits.

Greenstein

Because I began going down [Greenstein: to Wheaton] very frequently during the midyears of the war. There was gas rationing but he had this thing running all the time, this big wooden thing behind his motherís house, with the laundry hanging on it, and I liked him and we talked.

Sullivan

Can you sort of describe the set-up some more?

Greenstein

Well, he lived in a lower middle class suburb; he was a bachelor; he earned enough money to pay for his meals at his motherís house. And he put the rest in this wooden structure which carried the dish, and the dish was, I think, carefully and lovingly made. And being in radio and radio communication, maybe radar, Iím not sure, he was able to sneak tube some of these high-frequency tubes. And the first high frequency technology I ever saw was Groteís, with what I think were called "lighthouse tubes." Which are just little ziggurat-shaped things with sections, which are rather short and where the electron transfer time wasnít too long. And he would tell anybody about it, he wasnít supposed to have it, but he had one, or he had the best, or something like that. If you ever get to talk to him, youíll realize this peculiar- he absolutely wouldnít do anything in the straightforward conventional academic world, he couldnít. But he loved this kind of idea, that he could improve this technology, going to higher frequency. Didnít he go to 480, 160...

Sullivan

He started off at 3300 and got no signal, and he went down to 960 or 900 and finally went down to 480, no, I think the first time he skipped down to, gee, now Iím getting mixed up.

Greenstein

To a rather low frequency.

Sullivan

To 160, right.

Greenstein

I think itís 160 and...

Sullivan

It later went up to 480.

Greenstein

Yes, thatís what Iím saying.

Sullivan

And thatís where [Sullivan: 160] he detected it finally, but it made an amazing perseverance- to just keep going.

Greenstein

And every damned thing he did himself, he didnít have assistance- I mean, the recording mechanism was primitive, there were all kinds of dials and needles all over the place and getting the thing running was a major undertaking and tuning things up and hoping the tube wouldnít get noisy [Greenstein: before he had an interference-free night]. And stuff like that, because there were all kinds of limitations.

Sullivan

He had to work mainly at night, did he not, to avoid auto interference?

Greenstein

Yes. I can sort of feel that it was a rather ungainly, old-fashioned house. And I think there is a picture somewhere of the back of the house with the antenna there, and laundry strung between. But that is how I remember it. And we saw each other moderately frequently and I liked him, though he and I were very different. I was, I had started as a sort of a theoretician for those days, and I just found all of this fascinating, and although I may not have been in, and apparently donít really remember that 1940 paper, I know that any of the interest in the free-free that I had later, and you say that Henyey and Keenan did it in 1940, I thought it was later, and I think Iím involved in a paper somewhere there.

Sullivan

The 1946 one, yes.

Greenstein

What was that about?

Sullivan

I canít quite remember what the point...

Greenstein

Maybe the 1946 one had the lines then. But in any case, it was clear that something was going on, and Reber was finding it- he was no fraud, and in many ways, one would like to help him, but there was no practical way to help him in a university world. I tried.

Greenstein

Sullivan

Greenstein

Sullivan

He certainly talked with him a lot when Reber was talking courses and all.

Greenstein

Yes, the problem was, you see, Reber was a dropout from the university.

Sullivan

He did take some courses, didnít he?

Greenstein

Yes, yes.

Sullivan

Graduate courses in astrophysics?

Greenstein

Well, no, he couldnít have. All graduate courses in astrophysics were given at Yerkes. There was no astronomy department in town except for undergraduate teaching, and since he dropped out in the early 1940s, at the latest 1941 or something and went off into industry. I taught one elementary astronomy course there during the war, but Iím pretty sure he wasnít in it.

Sullivan

Where did he drop out from?

Greenstein

I think he tried to go through the University of Chicago.

Sullivan

Oh really?

Greenstein

Maybe he did make a year of it.

Sullivan

Well, I canít remember, I think once again that Keenan has told me that he did at least sit in on a couple... trying to learn some astrophysics.

Greenstein

He may have... but it would have to be at Yerkes, because there wasnít any undergraduate, I mean, there was one undergraduate course which during the war was taught by various people- I taught it I think in 1942, and Iím certain that Grote wasnít in it. But somehow we kept contact and he disappeared into mysteries of radar or radio, and I went off into optical design with Henyey. So there had to be a gap of a few years, but by 1944 when things looked a little bit more secure, I am fairly certain that I resumed contact with Reber. Now when is the next paper?

Sullivan

His 1944 paper presents the complete contour map.

Greenstein

And by then I was in fairly constant, of the order of once every few months, would be in touch and for all I know, have letters, but itís mostly visits.

Sullivan

What sort of reception did these 1940 and 1944 papers have in the astronomical- they were getting into the astronomical journals at least, thatís a start?

Greenstein

Thatís a start, and I donít think anybody disbelieved them. On the other hand, they didnít make any sense, because it was clear that if you turned his respectable units into temperatures, they were outside of anything we understood, and so in fact, the whole mystery is that the temperature of space in solid form is 3į; if you heat dust very fancily and if it has high absorptivity and low emissivity, you can get it up to 20į; in dust clouds, where you observe it in the infrared, itís up to 70į sometimes. No one had any idea really.

Sullivan

But what I meant...

Greenstein

The incredible amount of power that there was...

Sullivan

When really was it that the discrepancy was believed- that it must be a theoretical problem, because thereís some talk at that time about, "Well, itís a high temperature, but 100,000 Kelvins, it could be that Janskyís measurements are really a little bit high and Reberís are a little bit low."

Greenstein

But what was Reberís temperature corresponding to?

Sullivan

Oh, it was a lot less.

Greenstein

Because of the higher frequency.

Sullivan

Right. It was Janskyís that was the real problem.

Greenstein

Yes, well. With luck, if Reber had kept going, we could have explained it with our dust model- at higher frequency. But no, I honestly remember that just that kind of discussion and plotting, and I think there is this paper and I think I have it upstairs so maybe weíll stop for an instant. I remember diagrams with a couple of points representing power and the optically thin free-free emission.

Sullivan

Right.

Greenstein

And the points, and you just couldnít say they were on the curve.

Sullivan

Oh, yes. I agree...

Greenstein

Letís see the date on that. This worries me.

[Break]

Greenstein

Continuing, we do find it was in 1946 and I think from then on, as more measures were made people believed calibration in absolute units more, it was clear that a non-thermal theory was required. Thatís about where I would have to leave it...

A very important other thread hast to come in as to why astronomers after this period, with or without reference to the publication of the radio observations by the English, because very excited [Greenstein: about radio astronomy] and that was the realization of the importance of cosmic rays and magnetic fields in space. This arose largely, for me at least, through the interest of Enrico Fermi in the subject of the acceleration of the cosmic rays. He was, I would say, a rare visitor at Yerkes during World War II when he was engaged in the Manhattan District, he was a friend of Chandrasekhar and I remember an evening discussion with Fermi, giving sort of a semi-formal talk, about the mystery of the very large amount of energy in the cosmic radiation.

Sullivan

Cosmic rays.

Greenstein

Cosmic rays. And whether there were any cosmic ray electrons or not was then not known, but the question of the losses was very clear.

Sullivan

Now this was about what time?

Greenstein

This is before I left Yerkes, so thatís before 1948. So right after this 1946 period, people were worrying about acceleration mechanisms, betatron mechanism, moving magnetic fields trapping charged particles. Plasma physics existed already in a kind of sense, and I think this interested these good theoretical people in the question of whether you could make sense of the otherwise completely mysterious cosmic radiation, and the implication of a magnetic field, which meant something or other obviously about radio.

Sullivan

Right, and they were trying to tie it in with what was known about the interstellar medium at the time.

Greenstein

Thatís right. There was cloud structure in the interstellar medium, cloud-cloud interactions, and there was a great deal of abstract theory developed by Chandrasekhar on fluctuations in the velocity field of stars and the density field of interstellar gas, the existence of discrete clouds of gas. So that I would think that to be a very powerful motive for scientists in astronomy and physics, both to take the radio emission seriously, was that though there was no tie yet and this depended on the [Greenstein: Ginzburg-] Shklovsky idea, that it must be something else going on, and there was all the energy in the world available in the cosmic ray particles. If anybody [Greenstein: any cosmic ray physicist] had only said theyíre electrons, it would have been fine. Bruno Rossi came to Yerkes, in this interval I remember, gave a talk about the new knowledge on cosmic rays and he said, "The one thing that we can say with satisfaction, only thing that is of interest to astronomers about cosmic rays, is their place of origin; theyíre a realm for the physicistsí work." Completely screwball, just as wrong as he could be- just a year later you find interstellar polarization [Greenstein: magnetic fields in space] and things like that. So I think this is about a natural stopping point for me here.

Sullivan

Okay, but let me ask you though what your feeling is on why only you and Bok and maybe Struve saw the value of this early radio astronomy amongst optical astronomers? Do you have any ideas?

Greenstein

First of all, look at how few papers there were.

Sullivan

There were only Janskyís three papers when Reber began.

Greenstein

A couple of papers by Reber which showed the beginning of the picture of the Milky Way. I remember another optical gadget designed during the war made it possible to see radiation out to 2 microns. It was the lead sulfide photo conductive cell. And immediately people tried to look with it for the center of our Galaxy. In fact, there were rival and incorrect claims that they had seen it. At 1 micron it was hopeless, but they were good detectors; 2.3 microns gets through the atmosphere and the cell still worked.

Sullivan

So youíre saying there was interest in the non-optical regimes but they didnít know how to do anything though?

Greenstein

Right. 1 micron was the absolute limit of photographic photometry before the photoconductive devices. It was terribly bad. Photographic plates had 1,000 times lower sensitivity at 1 micron than they did at .5 microns. And they also had to be specially handled. So we [Greenstein: astronomers] were doing the best we could with the very limited technology. I donít know if you know this, but somewhere in the mid Ď30s or late Ď30s, a physics student at the University of Wisconsin was persuaded by a professor there who was using old-fashioned electrometers and some kind of Coblenz photoelectric surface to apply the methods of modern physics. And this fellow, whose name was Albert Whitford, who later became director of the Lick Observatory, is to my knowledge the first man who even used an amplifier for the photo cell for astronomy. It just seems so ridiculous, but on the other hand youíve got to remember how primitive science was. Itís all very well, the photoelectric cell was found by Einstein, understood ~1907-09, something. [Lee Alvin] DuBridge wrote a book about it in the Ď30s.